Use flag not working?

I was doing some work at my res tonight and heard my iron door open and close. I went down to my basement to investigate and found a player attempting to hide behind a wall before teleporting out. I got his name and checked all the flags on my res which were all still default so he shouldn't have been able to get past the door which opens and loses via a pressure plate. I immediately set a move flag on him but I'm worried If this person has the ability to steal from me or destroy my work. Any ideas?

i try to hide on peoples residence all the time not really too shadey most of the time its jusy neighbors being playful. use flag isnt really the one you gotta worry about anyways container is the killer. go hide on his res